I usually use 5 filler bars when direct combining wheat, especially if there are any green weeds in the field or conditions are tough. If conditions are ideal, as when combining clean swathed grain on a dry day, I remove all filler bars, which increases my capacity. For red clover, birdsfoot trefoil etc., I use filler bars for the entire concave, ensuring thorough thrashing and forcing all the material up to the walkers, where the losses are minimal in small seed crops.